A television receiver circuit requires a source of high direct-current voltages for connection to the cathode ray tube for the purposes of beam acceleration and of beam focusing. Voltages having values as large as 32 Kilovolts, for example, are generated through use of a circuit comprised of a flyback transformer, diodes, capacitors and resistors which converts the horizontal retrace pulses to direct current voltage.
A typical flyback transformer used in a high voltage circuit is comprised of a primary winding, optional auxiliary windings and a high voltage secondary winding. The secondary winding may be comprised of a plurality of series connected winding units connected through diodes. One end of the secondary winding is commonly coupled to a reference potential such as ground, the coupling sometimes made through a beam-current-sensing resistor. The other end of the secondary winding may be connected through a diode to a high-voltage terminal which, in turn, may be coupled through a high voltage lead to the cathode ray tube. The high-voltage terminal may also be connected to a capacitor and a bleeder resistor which are also coupled to reference potential. A focusing voltage or voltages may be tapped from the bleeder resistor and connected to an additional high voltage terminal or terminals for subsequent connection to the cathode ray tube and necessary filtering capacitors.
In order to minimize the probability of conduction paths being created by arcing, the mechanical construction of the high voltage circuit requires that those components which are charged during operation to high voltage potential be isolated to the maximum possible extent from components which are maintained at low potential. The design also requires that high voltage circuit components be surrounded where possible by non-conducting materials other than air, particularly where such components have small dimensions or sharply pointed configurations toward which free electrons in air might be attracted at speeds which cause break down or ionization of polarized molecules present in air.
The number of circuit components which require physical isolation from the television receiver chassis may be decreased, for example, by constructing the flyback transformer and the bleeder resistor in the same housing or container. Preferably, the container is constructed with high voltage output terminals located on surfaces of said container remote from that surface having low voltage terminals. The container is typically filled with an insulating material with high voltage breakdown characteristic. For example, non-conducting oil is commonly used in conjunction with a sealed metal container. Another insulating material commonly used is a synthetic resin which is poured under vacuum in liquid form to fill the open plastic container surrounding the high voltage circuit components. The synthetic resin is subsequently solidified by means of a curing process requiring temperature cycling.
Design and fabrication of the high voltage output terminals of such high voltage components presents particular difficulty. An external terminal on the container may, for example, be eliminated completely by internally connecting the high voltage lead or leads prior to filling or sealing said container. One problem with the use of that procedure is the necessity for sealing the container at the point of exit from said container to prevent liquid insulating material from escaping. Another problem results from the fact that the high voltage lead is exposed to damage by handling during production, shipping and assembly processes. It is, therefore, preferable to provide a high voltage terminal which may be located on a surface of the container remote from that surface having low voltage terminals, which does not allow leakage of insulating materials and which permits connection of high voltage leads during the final assembly stage of television receiver production.